The present invention relates to an improved process for producing Fischer Tropsch products through measuring oxygenate concentration using GC-AED.
The concentration of total oxygenates in Fischer-Tropsch products often needs to be maintained within established limits for optimal product characteristics. In addition, it may also be necessary to maintain the concentration of specific individual oxygenates within established limits. Therefore, to achieve the desired concentrations, the concentration of oxygenates, often specific individual oxygenates, in a Fischer-Tropsch product must be measured and controlled. The results from an analysis of oxygenates may be used to regulate operation of the Fischer Tropsch process. Accordingly, accurate measurement of oxygenates and control of their levels to desired set points are needed for efficient production of salable products from Fischer-Tropsch products.
There have been a variety of methods used to measure the concentration of oxygenates in Fischer-Tropsch products, including, elemental analysis, Infrared (IR), simple Gas Chromatography (GC), and GC coupled with mass spectrometry (MS). By way of example, U.S. Pat. No. 5,895,506 to Cook, et al. describes the use of Infrared (IR) techniques to monitor various oxygenate and olefin classes in Fischer-Tropsch products. IR techniques, however, have two disadvantages. First, they require calibration; calibration introduces error because the substance used for calibration may not behave exactly as the compounds in the sample. Second, IR techniques measure only the total concentration of each class of compounds (for example, alcohols, acids, etc.); therefore, they do not provide a distribution by carbon number. In performing and controlling a Fischer Tropsch process, a combined analysis by class and carbon number may be required.
GC may also be used to monitor oxygenate concentration. The basic science of gas chromatography has been known for over a century. GC separates different molecules in a mixture into components with different groups, typically sorted by molecular weight or boiling point. Various detectors can be used with GC. If a majority of the components in the mixture are to be measured, several detectors may be used, including a Thermal Conductivity Detector (TCD) or a Flame-Ionization Detector (FID).
When it is desired to measure a specific minority component in the mixture, it is preferable to use a detector that monitors the family of compounds that encompass the minority component. An example of such a detector is Gas Chromatography coupled with a Mass Spectrometry analyzer (GC-MS,) which can determine the specific components that elute from the GC at the same time. By way of example, U.S. Pat. No. 5,600,134 to Ashe et al. describes a method for controlling the bending of blend stocks using GC-MS. The method of Ashe requires a 10-step process for producing a training set of one or more known properties from reference samples. The training set provides a predicted MS value of the one or more properties against which MS information from the blend stocks may be compared. The training set is used to produce a predicted MS value of the desired properties for blend stocks and blend product samples. While GC-MS may be a good tool for identifying the general nature of compounds in a mixture, it can lack sufficient sensitivity for all operations.
In all of the above listed techniques, when control of specific individual oxygenate compounds at low levels is required, these techniques may be inadequate.
As control and measurement of specific individual oxygenate compounds at low levels may be important to producing salable products from Fischer Tropsch processes, there are needed techniques that can accurately and efficiently measure oxygenates and control their concentrations to selected set points.
The present invention relates to methods for producing a substantially paraffinic Fischer-Tropsch product or a blended Fischer Tropsch product comprising a selected oxygenate concentration, and if required, a selected oxygenate concentration of specific individual oxygenates. The methods of the present invention measure oxygenate concentration using GC-AED. The oxygenate measurements obtained using the GC-AED may be used to adjust and control various processes used to produce, upgrade, or finish Fischer Tropsch products to provide Fischer Tropsch products with a selected oxygenate concentration, and if required, a selected oxygenate concentration of specific individual oxygenates.
The present invention relates to a method for producing a substantially paraffinic Fischer-Tropsch product comprising at least one oxygenated species. In the method, a concentration of oxygenated species in the substantially paraffinic Fischer-Tropsch product is selected. A carbon number distribution of oxygenated species or a class of oxygenated species may also be selected. A Fischer-Tropsch synthesis is performed to provide a Fischer-Tropsch product stream. A substantially paraffinic product stream containing oxygenated species is isolated from the Fischer-Tropsch product stream. The substantially paraffinic product stream is purified, for example, by hydrotreating, hydrocracking, adsorption, extraction, and combinations thereof, to remove a portion of oxygenated species, to provide a substantially paraffinic Fischer-Tropsch product comprising at least one oxygenated species. The substantially paraffinic Fischer-Tropsch product is monitored for concentration of oxygenated species by GC-AED. The substantially paraffinic Fischer-Tropsch product may also be monitored for carbon number distribution or class of oxygenated species by GC-AED. The conditions of the purification are adjusted to ensure that the concentration of the oxygenated species in the substantially paraffinic Fischer-Tropsch product complies with the selected concentration. The conditions of the purification may also be adjusted to ensure that the carbon number distribution or class of the oxygenated species in the substantially paraffinic Fischer-Tropsch product complies with a selected carbon number distribution or class.
An additional aspect of the present invention relates to a method for producing a substantially paraffinic Fischer-Tropsch product comprising no detectable oxygenated species. In that method, a Fischer-Tropsch synthesis is performed to provide a Fischer-Tropsch product stream. A substantially paraffinic product stream containing oxygenated species is isolated from the Fischer-Tropsch product stream. The substantially paraffinic product stream is purified, for example, by hydrotreating, hydrocracking, adsorption, extraction, and combinations thereof, to remove the oxygenated species, to provide a substantially paraffinic Fischer-Tropsch product comprising no detectable oxygenated species. The substantially paraffinic Fischer-Tropsch product is monitored for concentration of oxygenated species by GC-AED. The conditions of the purification are adjusted to ensure that the concentration of the oxygenated species in the substantially paraffinic Fischer-Tropsch product is not detectable.
The present invention also provides a method for preparing a blended Fischer-Tropsch product comprising at least one oxygenated species. In the method a concentration of oxygenated species in the blended Fischer-Tropsch product is selected. A carbon number distribution of oxygenated species or a class of oxygenated species may also be selected. A Fischer-Tropsch synthesis is performed to provide a Fischer-Tropsch product stream. A substantially paraffinic product stream containing oxygenated species is isolated from the Fischer-Tropsch product stream, for example, by distillation. The substantially paraffinic product stream is blended with at least one non-oxygenate containing hydrocarbon stream to provide a blended product comprising at least one oxygenated species. The blended product is monitored for concentration of oxygenated species by GC-AED. The blended product may also be monitored for carbon number distribution or class of oxygenated species by GC-AED. The blending ratio is adjusted to ensure that the concentration of the oxygenated species in the blended product complies with the selected concentration and carbon number distribution. The blending ratio may also be adjusted to ensure that the carbon number distribution or class of the oxygenated species in the blended product complies with a selected carbon number distribution or class.
The selected concentration of oxygenated species may be between 100 and 5000 wppm (weight parts per million) on a water-free basis. Furthermore, the blended product may be used as diesel fuel or jet fuel. A further step of adding dispersants, detergents, anti-oxidants and ignition improvers to the blended product may also be included.
The at least one non-oxygenate containing hydrocarbon stream may be comprised of a non-oxygenate containing Fischer-Tropsch product stream which is isolated from the Fischer-Tropsch product stream, a conventional petroleum product, or a hydrotreated stream. If the at least one non-oxygenate containing hydrocarbon stream is comprised of a non-oxygenate containing Fischer-Tropsch product stream, the substantially paraffinic product stream may contain alcohol and the blended product may be used as a diesel fuel with reduced emissions. If the at least one non-oxygenate containing hydrocarbon stream is comprised of a hydrotreated stream, the blended product may be a pumpable syncrude.
In a further embodiment of the present invention, the concentration of oxygenated species, carbon number distribution of oxygenated species, class of oxygenated species or combinations thereof may be selected to improve the lubricity of the blended Fischer Tropsch product. Accordingly, the blending ratio of the Fischer Tropsch product stream comprising oxygenated species and the non-oxygenate containing hydrocarbon stream may be adjusted to achieve the improved lubricity.
An additional aspect of the present invention relates to an integrated method for preparing a Fischer-Tropsch product comprising at least one oxygenated species. In the integrated method the substantially paraffinic product stream comprising at least one oxygenated species to be blended with at least one non-oxygenate containing hydrocarbon stream is produced using GC-AED to monitor the concentration of the oxygenated species. A carbon number distribution of oxygenated species or a class of oxygenated species may also be monitored using GC-AED. This substantially paraffinic Fischer-Tropsch product comprising at least one oxygenated species is blended with at least one non-oxygenate containing hydrocarbon stream. This blending is also monitored using GC-AED to ensure that the blended product has a selected concentration of oxygenated species. This blending may also be monitored using GC-AED to ensure that the blended product has a selected carbon number distribution or a class of oxygenated species.
Definitions:
The following terms will be used throughout the specification and will have the following meanings unless otherwise indicated.
xe2x80x9cConventional petroleum productxe2x80x9d means any products from a conventional source, i.e. not synthetically produced. Conventional petroleum products include, for example, petroleum, diesel fuel, solvent, jet fuel, naphtha, lube base stock, lube base stock feedstock, and lube base oil.
xe2x80x9cHeteroatomxe2x80x9d refers to an atom other than carbon or hydrogen such as sulfur, oxygen, nitrogen, and the like.
xe2x80x9cHydrocarbonaceousxe2x80x9d means containing hydrogen and carbon atoms and potentially also containing heteroatoms, such as oxygen, sulfur, nitrogen, and the like, as well.
xe2x80x9cHydrocarbonaceous productxe2x80x9d means any product containing hydrogen and carbon atoms, and may also contain heteroatoms such as oxygen, sulfur, nitrogen, and the like.
xe2x80x9cHydroprocessingxe2x80x9d means a process wherein a hydrocarbonaceous product is contacted with hydrogen over a catalyst at pressures greater than atmospheric. Examples include hydrotreating, hydrocracking, hydroisomerization, and hydrodewaxing.
xe2x80x9cHydrotreated streamxe2x80x9d means a hydrocarbonaceous stream that has been hydrotreated to remove impurities, such as elemental sulfur, nitrogen, or oxygen or compounds containing, sulfur, nitrogen, or oxygen. The hydrocarbonaceous stream may be a Fischer-Tropsch product stream or a convention petroleum product stream.
xe2x80x9cNon-oxygenated hydrocarbon streamxe2x80x9d refers to a hydrocarbonaceous product stream comprising less than approximately 10 ppm oxygen as oxygenates. For the specific example of a diesel with an average carbon number of about 12, 10 ppm oxygen as oxygenates corresponds to approximately 100 ppm oxygenates. The non-oxygenated hydrocarbon stream of the present invention may be isolated from a Fischer Tropsch product stream, may be a conventional petroleum product stream, or may be a hydrotreated stream.
xe2x80x9cNo detectable oxygenated speciesxe2x80x9d means that any individual specific oxygenated species is below 1 ppm as oxygen.
xe2x80x9cSubstantially paraffinic productxe2x80x9d refers to a product comprised of at least 50% paraffins.
xe2x80x9cSyngasxe2x80x9d is a mixture that includes hydrogen and carbon monoxide. In addition to these species, others may also be present, including, for example, water, carbon dioxide, unconverted light hydrocarbon feedstock, and various impurities.
xe2x80x9cOxygenatexe2x80x9d means a compound that includes at least one oxygen atom. Oxygenates include for example, alcohols, ethers, carboxylic acids, and the like.
xe2x80x9cClass of oxygenate speciesxe2x80x9d means classes into which oxygenates may be separated. For example, alcohols, ethers, carboxylic acids, and esters are specific classes of oxygenated species.
xe2x80x9cIntegrated Processxe2x80x9d means a process comprising a sequence of steps, some of which may be parallel to other steps in the process, but which are interrelated or somehow dependent upon either earlier or later steps in the total process.